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 Which is better metal halide or black light?

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Flexoto

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Number of posts : 61
Location : Pampanga
Member since : 2007-06-15

PostSubject: Which is better metal halide or black light?   Sun Jul 08, 2007 12:40 am

Which is better source of light for platemaking metal halide or black lights? Where can I buy metal halide bulb? How much does it cost? How many bulbs and watts required to produce satisfactory image on plate?

Thank you.
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presstech

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Age : 69
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Member since : 2007-05-29

PostSubject: Re: Which is better metal halide or black light?   Sun Jul 08, 2007 10:40 pm

Metal halide is definitely better than black light. This is the reason why most late model branded platemakers use metal halide. The only platemakers I have seen using black flourescent lights are low cost locally made units.

During the early 80's, I used a platemaker with fluorescent UV black lamps. The main problems encountered were enlarged halftone dots and dots with soft edges.

Normally a 1,000 watts metal halide lamp is used for medium sized plates. Exposure would be about 40 seconds, depending on the distance between the lamp and the plate. Proper exposure time can be determined by using a device called sensitivity guide. This can be purchased from Tritan for P450.

Metal halide lamps for platemakers are difficult to find. They come in 2 parts: the bulb and the ballast/igniter. I know an electrician who can assemble a 400 watt metal halide lamp. This lamp will give a good exposure in 2 minutes. He is Raffy Sandicho. His contact info is listed at www.philprinting.com in the Opportunities section.

The best option, I think, is to buy a second hand branded unit from a dealer. You can get a good one (size: 22 x 30) for about P80,000.
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Flexoto

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PostSubject: Re: Which is better metal halide or black light?   Mon Jul 09, 2007 11:33 pm

Definitely the best option is to buy a ready to use second hand platemaker but unfortunately I cannot afford to do that at this point as I am in a tight budget. I am presently using halogen and want to replace it with metal halide lamp. Though at first I thought of replacing it with black light because it is easier to install and I think cheaper. I tried to contact Raffy but I think the number in www.philprinting.com is no longer active.
I canvassed for metal halide, a 400watts complete set (with housing and ballast/igniter) costs P3900. I was told it is being used to light billboards. Before I buy it I would like to ask the following:
1. Is 400watts good enough for a 20x25 platemaking frame?
2. What is the suggested distance from the plate?
3. How much more or less is the cost if I ask somebody to assemble it for me?
4. I find the housing big and heavy and the distribution of light is not suited for platemaking. Do you recommend if I ask somebody to assemble it for me? Or is there readily assembled?
Thank you.
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presstech

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Number of posts : 256
Age : 69
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PostSubject: Re: Which is better metal halide or black light?   Tue Jul 10, 2007 2:10 am

I had 2 fliptop platemakers with defective lamps converted to the 400 watts metal halide. The exposure time was about 2 minutes with a distance of 4.5 to 5 feet between the lamp and the plate. Both units had 20 x 28 frames. The quality of the images were similar to that produced by the original 1000 watts lamp. I didn't use the lamp with housing that you saw. The components were purchased separately and then assembled using the original platemaker lamp reflectors. I think you can assemble this yourself to save on cost.

This is a photo of the bulb:


These are the igniter and ballast:
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presstech

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PostSubject: Re: Which is better metal halide or black light?   Tue Jul 10, 2007 2:16 am

By the way, since the lamp takes a while to reach maximum brightness, you should install a shutter to cover the lamp's light while the brightness is building up. You can probably make a metal cover that you can manually slide open to expose and slide close to stop exposure. If you are planning to make a second exposure, do not power off the lamp; because it will not turn on right away if it's still hot.
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Flexoto

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PostSubject: Re: Which is better metal halide or black light?   Tue Jul 10, 2007 11:01 am

Thanks Presstech, I guess this is all I need to complete my platemaker. I'll inform you about the result as soon as I completed it.
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